Fin for surf craft

ABSTRACT

A fin ( 410 ) with a discrete structural strand layer ( 420 ) that may include high tensile carbon fibre strands ( 422, 424 ) and high tensile strength and toughness Kevlar ( 426 ) strands. These structural strands may have a tensile strength substantially greater than the other materials typically used in a fin body. The structural strand layer ( 420 ) provides an economic and ready technique to vary and control a stiffness characteristic of the fin in a variety of directions or about a variety of axes of rotation; without varying the other common components that may be used in a fin body, for example core ( 412 ), layers of fibreglass fabric ( 414 ) and/or resin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fins and methods for making them as maybe applied to surf craft such as surfboards, windsurfers, paddleboards,wave and surf skis, kite-boards, wake boards and the like.

2. Description of the Art

Surf craft (including surfboards) often have one or more fins located onan underside of the surf craft that, for example, may be used forstability, controlling direction and facilitating turning of the surfcraft. In addition surfboards may have multiple fins with differentfunctions, for example an uppermost side fin with a curved or airfoilprofile may function so as to provide to provide lift when the surfboardis travelling across the face of a wave and the uppermost side fin islocated within the face of the wave. It also follows that extraacceleration and drive to the surfboard results.

Fin/s of turning surf craft may experience substantial side ways andother forces to the face of the fin/s. How the fin/s respond to thesesideways and other forces in turns and other manoeuvres may stronglyaffect the performance of the surf craft for a particular set of surfconditions. The construction of a fin may in particular affect itsresponse to sideways and other forces in use.

Current surfing trends, particularly in competitive surfing, involvemultiple, high speed, sharp turns of a surfboard whilst a wave is beingridden. Such manoeuvring of a surfboard places very significant forceson the fins of the surfboard. Under such forces, the fins tend toexperience bending (e.g. between the base and the tip of the fin) andtwisting (e.g. between the leading and trailing edges of the fin). Thefin's ability to return sharply to its normal state following theremoval of the experienced force (e.g. via a turn) affects theperformance of the fin and, consequently, the surfboard.

Commonly available fins for surfboards may be a composite structure oflayers of bi-directional fibreglass fabric imbedded in a suitable resinand then moulded and/or shaped to the form of a fin. The word“bi-directional” in the following is taken to include the direction ofthe fibreglass strands within the closely woven fabric. The fibreglassstrands being often made up of multiple fibres or filaments offibreglass. Bi-directional fibreglass or other reinforcing fabric oftenhas a basket weave pattern where the strands are closely interwovenorthogonally to form the fabric.

The reinforcing fibreglass fabric together with the impregnating resinor other suitable material typically determines the physical propertiesof the fin in terms of, by way of example, the stiffnesscharacteristics, bending resistance, twisting resistance and/orflexibility of the fin to sideways and other forces in a turn or othermanoeuvres. However for typical fins, varying the stiffnesscharacteristics, flexibility or other such properties of the fin in aneasily manufacturable and controllable fashion is difficult due to themany layers of reinforcing fabric with impregnating resin matrixcontributing to the stiffness or flexibility across the fin. There isalso the additional limitation of what is commercially available inreinforcing fabrics and the strand materials forming them.

None of these prior art fin devices and methods of construction for finsprovides an entirely satisfactory solution to the provision of fins forsurf craft where the desired stiffness characteristics and otherphysical properties may be varied in a controllable fashion, nor to theease of providing a convenient and reliable way of manufacturing finshaving different degrees of stiffness or other desirable physicalproperties.

SUMMARY OF THE INVENTION

The present invention aims to provide an alternative method forconstructing a fin in which the stiffness characteristics and otherphysical properties of the fin may be better controlled and/or varied aswell as to the provision of fins with different, controlled stiffnesscharacteristics which overcomes or ameliorates the disadvantages of theprior art, or at least provides a useful choice.

In one form, the invention provides a fin for surf craft comprising: afin body and at least one layer of structural strands, located withinthe fin body; wherein the structural strands are in one or morenon-woven arrangements; and the structural strands have a physicalproperty greater than a corresponding physical property of othermaterial forming the fin body; and wherein the physical property isselected from at least one of a toughness, a tensile strength, anelastic moduli and a Youngs modulus. Preferably at least a portion ofthe structural strands extend substantially from a base portion to a tipportion of the fin. Preferably at least a portion of the structuralstrands extend substantially from a base portion to a leading edgeportion of the fin. Preferably at least a portion of the structuralstrands extend substantially from a leading edge portion to a trailingedge portion of the fin. Preferably at least one layer of structuralstrands in one or more arrangements is located within the fin body suchthat the at least one layer of structural strands is substantiallyparallel to opposing faces of the fin.

Preferably the structural strands of at least one layer aresubstantially parallel to each other. Preferably in a first arrangement,the parallel structural strands are generally parallel to a sweep angleof the fin. In an alternate first arrangement, the parallel structuralstrands are at a first angle to a sweep angle of the fin, the firstangle being in the range of up to 20 degrees, more preferably theparallel structural strands are at a first angle of approximately 10degrees to a sweep angle of the fin. Preferably a second arrangement theparallel structural strands are at a second angle to the vertical of thefin, the second angle being in the range of 20 to 40 degrees morepreferably the parallel structural strands are at a second angle ofapproximately 30 degrees to the vertical of the fin. Preferably a thirdarrangement, the parallel structural strands are generally vertical.

Preferably in a primary arrangement, the parallel structural strands aregenerally perpendicular to a sweep angle of the fin. Preferably in asecondary arrangement, the parallel structural strands are at a firstangle to a sweep angle of the fin, the first angle being in the range of20 to 40 degrees, more preferably the parallel structural strands are ata first angle of approximately 30 degrees to a sweep angle of the fin.Preferably in a tertiary arrangement, the parallel structural strandsare generally vertical.

Preferably at least one layer of structural strands comprises of aplurality of structural strands extending from at least onesubstantially common point in a substantially radial formation.Preferably at least one substantially common point is adjacent the baseportion of the fin. Preferably at least substantially common point isadjacent at least one of a leading edge portion and a trailing edgeportion of the fin.

Preferably at least one structural strand comprises of a plurality offilaments. Preferably at least one structural strand is made of at leastone of carbon fibre, Kevlar, aramide, natural fibres and syntheticfibres. Preferably at least one structural strand has a tensile strengththat is at least 1.5 times greater than the tensile strength of theother material forming the fin body. Preferably at least one structuralstrand has a Youngs modulus that is at least 1.5 times greater than aYoungs modulus of the other material forming the fin body. Preferably atleast one structural strand has a toughness that is greater than atoughness of the other material forming the fin body. Preferably atleast a portion of the structural strands comprises unidirectionalfilaments in a ribbon configuration. Preferably at least a portion ofthe structural strands have a width in the range of 0.5 to 3 mm.Preferably at least a portion of the structural strands has a width inthe range of 1 to 2 mm. Preferably at least a portion of the structuralstrands comprises of at least about 3,000 filaments per structuralstrand.

Preferably a spacing between at least a portion of the structuralstrands is less towards the base portion compared with the tip portionof the fin. Preferably a spacing between at least a portion of thestructural strands is in the range of 1 to 30 times a width of onestructural strand, more preferably a spacing between at least a portionof the structural strands is in the range of 4 to 13 times a width ofone structural strand. Preferably a spacing between at least a portionof the structural strands is in the range of 4 to 15 mm, more preferablya spacing between at least a portion of the structural strands is in therange of 9 to 13 mm.

In one form, the invention provides a fin for surf craft comprising: afin body; and at least one layer of structural strands, located withinthe fin body; wherein the structural strands are in one or more wovenarrangements that are at least one of an open weave and a scrim; whereinthe structural strands have a physical property greater than acorresponding physical property of other material forming the fin body;and wherein the physical property is selected from at least one of atoughness, a tensile strength, an elastic moduli and a Youngs modulus.Preferably, further including a core structure located within the finbody. Preferably at least one layer of structural strands in one or morearrangements is embedded within a body of the fin such that the layer ofstructural strands is substantially parallel to a face of the corestructure. Preferably at least one layer of structural strands arelocated intermediate the core structure and at least one of the opposingfaces of the fin. Preferably the core is at least one of a foam corestructure and a solid, non-foam core structure. Preferably at least aportion of the core structure is made of at least one of PVC foam,polyurethane foam, resin impregnated fibreglass, hardened resin,polyester mat, microspheres, plastic, bamboo and wood.

Preferably further including at least one layer of unidirectional carbonfibre fabric towards a base portion of the fin body, more preferably atleast one layer of carbon fibre fabric is located about a periphery ofthe fin body.

Preferably a sweep angle of the fin is in the range of 20 to 60 degrees.

In yet another form, the invention provides a method of controlling afin physical property for a surf craft, the method comprising: selectingone or more structural strands having a structural strand physicalproperty greater than a corresponding physical property of othermaterials in a body of the fin; selecting a number of structural strandsto provide the fin physical property; providing a layer of thestructural strands in one or more arrangements; and embedding the layerof structural strands in the body of the fin; whereby varying at leastone of the structural strands selection, the number of structuralstrands or the arrangement of the structural strands varies the finphysical property; and wherein the fin physical property is selectedfrom at least one of: a stiffness characteristic, a bending resistance,a twisting resistance, a resistance to a deflection, a flexibility and ahigh elastic recoil; and wherein the structural strand physical propertyis selected from at least one of: a toughness, a tensile strength, anelastic moduli and a Youngs modulus. Preferably the step of providing alayer of structural strands includes the use of a template to locate oneor more structural strands of one or more arrangements. Preferably thestep of using a locating template further includes providing at leastone of pins, adherents and securing systems to locate one or morestructural strands. Preferably the step of using a locating templatefurther includes the steps of: providing one or more reliefs machinedinto the template, and laying individual structural strands intorespective reliefs to form a three dimensional structural strand layer.Preferably the step of providing a layer of structural strands includesthe use of a numerically or a computer controlled machine to locate oneor more structural strands of one or more arrangements.

Preferably the step of providing a layer of structural strands furtherincludes a step of: configuring the arrangement of structural strands ina layer to vary the fin physical property. Preferably further includingproviding one or more structural strands largely parallel to a sweepangle of the fin such that the fin is provided with an increasedresistance to a twisting of the fin. Preferably further includingproviding one or more structural strands at a first angle of up to 20degrees to a sweep angle of the fin to provide the fin with an increasedresistance to a twisting of the fin. Preferably further includingproviding one or more structural strands at a second angle in the rangeof 20 to 40 degrees to the vertical axis of the fin such that the fin isprovided with an increased resistance to a deflection from the verticalaxis.

A fin for surf craft produced according to the methods described above

In an alternate form, the invention provides a fin for surf craftsubstantially as described herein and a method of controlling astiffness characteristic or other desired physical property of a fin fora surf craft substantially as described herein.

Further forms of the invention are as set out in the appended claims andas apparent from the description.

DISCLOSURE OF THE INVENTION Brief Description of the Drawings

The description is made with reference to the accompanying drawings; ofwhich:

FIG. 1 is a perspective, representative view of a surfboard

FIG. 2 is a side elevation view of a fin from the surfboard of FIG. 1.

FIG. 3 is a bottom view of a fin of FIG. 2.

FIG. 4 is a “peel-away” or partially exploded perspective view of a sidefin in an embodiment of the present invention.

FIG. 5 is a side elevation view of the fin embodiment of FIG. 4.

FIG. 6 is a plan view of a template board.

FIG. 7 is a schematic showing a layup of three arrangements of astructural strands layer embodiment on the template board.

FIG. 8 is an enlarged view of the circled region in FIG. 7.

FIGS. 9 to 13 are respective side, plan, end and bottom elevation viewsof a FEA analysis of homogeneous fin under an applied force.

FIGS. 14 to 18 are the same elevation views of the fin of FIGS. 9 to 13with no force applied.

FIGS. 19 to 42 are to further embodiments of the invention in sideelevation views only, unless otherwise indicated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective, representative view of a surfboard 110 toillustrate the main features associated with surfboards in general. Thesurfboard 110 has a board 112 with a deck 114 that the surfer stands on.The board 112 has a nose 116, a tail 118 and two rails 120 defining thegenerally longitudinal edges of the board 112. To an underside 122 ofthe board 112 one or more fins 124, 126 are typically attached, usuallytowards the tail 118 but for high performance surfboards and other surfcraft the fins may be located at a variety of locations along theunderside of the board. The surfboard 110 illustrated as an example hasthree fins 124, 126 in a “thruster” configuration however surfboards mayalso have one, two (“twin fin”), four or more fins in a variety ofconfigurations. An outside face 310 and inside face 312 of the side fin124 are described in detail below with respect to FIG. 3.

The overall general axes of orientation to a surfboard 110 may be avertical axis 128, a transverse or “sideways” axis 130 and alongitudinal or “stringer” axis 132.

FIG. 2 is a side elevation view of a fin 124, 126 to additionallyillustrate the main features associated with a fin. The fin may have abase 210 with attachment features, tabs or attachment means 212 whichenable the fin 124, 126 to be suitably attached or secured to theunderside 122 of the board 112. It will be readily appreciated thatthere may be a variety of attachment or securing means for a fin to anunderside of a board. The fin may have a leading edge 214 that istowards the nose 116 of the board 112 and a trailing edge 216 which istowards the tail 118. A tip 218 of the fin may be also used to define asweep angle 220 of the fin, as shown with the dashed lines, with respectto the vertical axis 128. For reference in the following detaileddescription a rotation or twist 222 about the vertical axis 128 of thefin 124, 126 may occur in use. Alternatively a rotation or twistcomponent/s may occur about an axis corresponding to the dashed line inFIG. 2 corresponding to the sweep angle from the base 210 to the tip 218of the fin. A vertical height or depth 224 dimension from the base 210to the tip 218 of the fin may also be defined as shown in FIG. 2. Thebase 210 may have a base length 226 dimension as shown in FIG. 2.

FIG. 3 is a bottom view of the fin in FIG. 2. The fin shown is anexample of a side fin 124 where an outside face 310 may be more curvedthan an inside face 312 of the fin 124. The outside face 310 of the fin124 corresponds to the face closest to the rail 120 of the board 112whilst the inner face 312 is the opposing face to the outer face 310.The different respective curvatures of the faces 310, 312 are configuredto form an airfoil which induces a sideways hydrodynamic force upon theside fin 124 and thereby providing lift, as the fin travels through awave and in particular across the face of a wave.

The side fin/s 124 and/or centre fin/s 126 may also experience a varietyof other hydrodynamic forces upon them during turns and complexmanoeuvres which may cause them to deflect and/or twist from their atrest positions.

FIG. 4 is a “peel-away” or partially exploded perspective view of a sidefin 410 in an embodiment of the present invention. For reference FIG. 5is a side elevation view of the fin 410 of FIG. 4, viewing the outsideface 310. In FIG. 4 a core 412 may optionally be included to reduce theweight of the fin, provide positive buoyancy in water and/or as furtherdescribed below. The core 412 may be a solid (non-foam) or a foam core,where a foam core includes air pockets within that may be partially orfully filled with impregnating resin. Solid cores may be made of resinimpregnated fibreglass, hardened resin, plastic, bamboo or wood.Alternatively, foam cores may be PVC foam, polyurethane (PU) foam or anadvanced foam core materials such as Lantor Coremat as described atwww.lantor.nl. The Lantor Coremat being a nonwoven polyester matcontaining microspheres. Layers of fibreglass fabric 414 may optionallybe present, the two layers illustrated in FIG. 4 being onlyillustrative. Many more layers of fibreglass fabric 414 may be presenton either side of the core 412 depending on the particular fin type andshape being designed/manufactured. An optional outer layer of blackpolyester veil 416 for each face 310, 312 of the fin may be included topromote resin flow, as well as improve the external finish andappearance of the fin 410. A further, optional outer layer ofuni-directional carbon fibre fabric 418 may be included near the base210 of the fin 410; possibly extending to the attachment means 212 toimprove stiffness and strength at those parts of the fin body.

A description of the commonly available materials used to manufacturefins as illustrated in FIG. 4 is provided in the following by way ofexample only. The fibreglass fabric 414 may be of 6 oz, close, plainweave or of other readily available fibreglass reinforcing fabrics. Thecore may be a PVC foam of a 1.3 to 2.5 lb/cubic foot density PVC foam,black silk or polyester veil and urn-directional carbon fibre fabric of300 gsm (grams/metre squared) weight. It will be readily appreciatedthat these commonly available materials may be varied in terms ofwhether they are included in a fin body and what may be selected fortheir use as would be exercised by a person skilled in the art of surfcraft, surfboards in particular, design and manufacture.

The embodiment of the invention in FIG. 4 shows a structural strandlayer 420 that may include high tensile carbon fibre strands 422, 424and high tensile strength and toughness Kevlar 426 strands. Structuralstrand examples are described in detail further below. The layer ofstructural strands 420 features structural strands which may have atensile strength substantially greater than the other materialstypically used in a fin body. The use of a discrete structural strandlayer 420 provides an economic and ready technique to vary and control astiffness characteristic physical property of the fin in a variety ofdirections or about a variety of axes of rotation; without varying theother common components that may be used in a fin body.

The term “stiffness characteristic” as a physical property in thefollowing detailed description and claims is taken to include:

-   -   The resistance of the fin to deflection or twist forces in a        variety of directions. Or in other words a twisting resistance        and/or a bending resistance.    -   The flexibility of the fin in a variety of directions or about a        variety of axes.    -   High elastic recoil or restoration of the fin after a force or a        twist is applied to it is released. For example the snapping        back of the fin after it has been deflected due to forces        applied during a turn or complex manoeuvres. In other words        energy or work put into the fin in a turn is returned, with        little or no loss, to the surfer or rider of a surf craft at the        completion of a turn.    -   Stiffness, resilience and/or flexibility physical properties        imparted to the fin by the combination of various materials of        various tensile strengths, elastic moduli and other properties        into the fin construction.

In addition toughness as a physical property in the following detaileddescription and claims is taken to include a comparatively moderatetensile strength material with improved ductility, for exampleKevlar/aramide fibres may have a higher toughness compared with carbonfibres. Fibres with superior toughness have a high degree or resistanceto repeated twisting and/or bending.

The carbon fibre strands 422 may be largely parallel to the sweep 220 ofthe fin 410 or offset from the sweep angle by up to 20 degrees,preferably approximately 10 degrees in the example shown in FIG. 4. Thestructural strands 422 may be introduced as a first arrangement tocontrol how much the fin resists twisting, in particular about thevertical axis. Or in other terms how much energy is retained or storedin the fin from its twisting in use. The use of more structural strandsin the first arrangement will increase the resistance to twisting by thefin. The carbon fibre strands 424 that are offset to the vertical by 20to 40 degrees, preferably approximately 30 degrees, may be introduced asa second arrangement to modify how much the fin resists deflection fromthe vertical axis. Preferably the direction of the offset to thevertical for strands 424 is towards the fin leading edge 214. The use ofmore structural strands in the second arrangement will increase theresistance to deflection from the vertical axis for the fin. As ageneral comment, the stiffness characteristic that may be imparted by astructural strand, to a fin, being largely in the longitudinal/lengthdirection of the strand and proportional to the number of structuralstrands and the structural strand physical properties. The largelyvertical Kevlar strands 426 may be additionally introduced as a thirdarrangement to improve the stiffness characteristic as well as thetoughness and strength of the fin so that it may resist breakage.

A description of the structural strands used in the structural strandlayer 420 is provided in the following by way of example only. “3 k”(3,000 filaments per strand) unidirectional carbon fibre strands in alargely ribbon form, “toe” form, may be used. “3 k” unidirectionalKevlar or Aramide equivalents strands in a substantially ribbon form maybe used. Typically the ultimate tensile strengths of carbon andKevlar/Aramide fibres may be at least 1.5 times or 2 times (2×) or morethan commonly used fibreglasses such as E-glass and more than the othercommonly used materials in a fin body. Similarly the elastic moduli suchas Youngs modulus for carbon fibre and Kevlar/Aramide equivalents may beat least 1.5 times (1.5×), 2 times, 5 times or more than commonly usedfibreglasses such as E-glass and more than the other commonly usedmaterials in a fin body. The width of ribbon strands may be in theapproximate range of 0.5 to 3 mm or more preferably in the range of 1 to2 mm. The ribbon strands may have a thickness. The thickness of a ribbonstrand may be greater than 0.1 mm. Natural fibres and synthetic fibres(in addition to those mentioned already) may also be suitable withappropriate resin, plastic and/or binder systems. It will be readilyappreciated that these structural strand materials may be readily variedin terms of what may be selected for their use as would be exercised bya person skilled in the art of surf craft, surfboards in particular,design and manufacture. Furthermore the person skilled in the art wouldbe guided in their choice of structural strands by their superiorphysical properties in comparison to the other materials used in theconstruction of the fin; for example carbon fibre over fibreglass andvia a property such as tensile strength.

In one embodiment a layer of the structural strands may be fabricated byuse of an aluminium template 610 as shown in FIG. 6 in plan view. Thetemplate may have marked upon it the outline 612 of the fin 410, markerlines 614 for the location for the carbon fibre strands 422 in the sweepdirection or angle 220, marker lines 616 for the carbon fibre strands424 that may be 30 degrees from the vertical axis of the fin outline 612and marker lines 618 for the Kevlar strands 426.

FIG. 7 shows the layup of three arrangements of structural strands 422,424, 426 on the template board 610 to form a layer of structural strands420. A first parallel arrangement 710 of carbon fibre strands 424 thatare offset approximately 30 degrees to the vertical axis of the finoutline 612 may be hand laid first. The spacing between the parallelcarbon fibre strands 424 may be chosen to be in the range of 9 to 13 mmfor a fin of approximate depth 224 of 100 mm. A second parallelarrangement 712 of Kevlar strands 426 may then be laid down. The spacingbetween the parallel Kevlar strands 426 may be chosen to be in the rangeof 4 to 8 mm for a fin of depth 224 of 100 mm. The Kevlar arrangementmay then be followed by a third parallel arrangement 714 of carbon fibrestrands 422 that may be in the sweep angle 220 direction of the finoutline 612. The spacing between the parallel carbon fibre strands 422may be chosen to be in the range of 9 to 13 mm for a fin of depth 224 of100 mm. It will be readily appreciated that the numerical values forstrand spacing and orientation are to obtaining a particular stiffnesscharacteristic and are only illustrative. For example a fin ofapproximate depth of 111 mm may have a spacing between the parallelcarbon fibre strands 424 in the range of 9 to 15 mm or more preferablyin the range of 10 to 12 mm. Other examples are given below with respectto FIGS. 19 to 42, where the relative, proportional and/or angularrelationships between the structural strands are shown.

To aid in the laying up of the strands for each arrangement, pins orother locating, fixing, securing or otherwise aid devices (not shown)may be used at the periphery of the template 610 to locate and/or securethe strands in a desired arrangement. More complex arrangements orconfigurations may also be laid up and these are described below indetail with respect to FIGS. 19 to 42. For these more complexarrangements further locating/securing systems such as pins, adherentsand the like may be used to facilitate the forming of more complexarrangements of the structural strands.

In the course of laying up the arrangements 710, 712, 714 of structuralstrands the individual strands may be impregnated with a suitable resinor binder in order that overlapping structural strands may be adheredtogether. FIG. 8 is an enlarged view of the circled region in FIG. 7.FIG. 8 shows the resin or binder 810 adhering overlapping 812 structuralstrands 422, 424, 426 together. The template board 610 may be pre-coatedwith a release agent to prevent the adhering of the resin or binder 810to the template 610.

In the above example of forming a structural strand layer 420 the layeris not woven, that is the structural strands are not interlaced. Inaddition the layer is in the form of a scrim with clear apertures 814.From the above examples of ribbon strand widths and strand spacing therelative clear aperture may be from approximately 1 to 30 times (1×-30×)one ribbon strand width or more preferably from 4 to 13 times (4×-13×)one ribbon strand width. In further embodiments of the structural strandlayer, described in detail below with respect to FIGS. 19 to 42, thestructural strands from various arrangements may have some or all oftheir strands interlaced in some fashion to form a woven arrangement orscrim for the structural strand layer.

The technique for forming the structural strand layer may also beadapted to a computer or numerically controlled apparatus to manufacturethe structural strand layer. A numerically controlled (NC) machine(and/or computer controlled) may be particularly suited for thearrangements/configurations described below with respect to FIGS. 19 to42. For example an embroidery machine may be adapted to lay out thestructural strand layer.

The scrim structural strand layer may then be die or otherwise cut intothe desired outline which for the example above is the full outline 612of the fin. The structural strand layer may then be appropriatelyinserted into a mould of a fin with the other fin components, forexample described above with respect to FIG. 4. In order to form the finbody a suitable resin system or plastic together with possible additivessuch as fillers and/or colour agents may then be injected into the mouldto impregnate all the reinforcing fabrics and the structural strandlayer to form the fin body. Resin Transfer Moulding (RTM) is one commonexample of a mass production technique for forming the fin. Compressionmoulding may also be used, by way of example.

Alternatively the scrim structural strand layer may be directly removedfrom the template board 610 without cutting to the fin outline 612. Thescrim structural strand layer may then be appropriately incorporatedinto a traditional fin panel of fibreglass sheet and resin, formed bymachine and/or hand. A desired fin may then be machine cut (for exampleNC machine) from the fin panel incorporating the structural strandlayer. The machine cut fin may then be hand finished and polished.

Without wishing to be bound by theory, Finite Element Analysis (FEA) maybe readily done for a typical homogeneous fin (not incorporating astructural strand layer). FIGS. 9 to 13 show the results of an FEA modelof a homogeneous fin being subjected to a force applied to the normal offace 312 of a side fin 124, 410. The applied force simulates thesideways force that a side fin may experience when: travelling acrossthe face of a wave, in a manoeuvre and/or when a fin is at a high angleof attack to the bulk fluid flow stream under the surfboard. FIG. 9 is aside view, FIG. 10 is a plan view, FIG. 11 is an end view, FIG. 12 is abottom view and FIG. 13 is a front view. Contour lines 910 to 918 havebeen placed on each of the views to show the amount of horizontaldisplacement of the fin, from its rest position, by an applied force.Contour line 910 is approximately 20 mm at the tip 218, contour line 912is approximately 13 mm, contour line 914 is approximately 10 mm, contourline 916 is approximately 3 mm and contour line 918 at the secured base210 is 0 mm. For comparison purposes FIGS. 14 to 18 are views of thesame fin with no force applied. FIG. 14 is a side view, FIG. 15 is aplan view, FIG. 16 is an end view, FIG. 17 is a bottom view and FIG. 18is a front view.

It is apparent from FIGS. 9 to 18 that a side fin travelling along theface of a wave, or otherwise as per above, may bend sideways in thedirection of the transverse axis 130 as well as twisting/rotating aboutthe vertical axis 128. Altering the stiffness characteristic of such afin by incorporating a structural strand layer may readily affect theresponse of the fin to applied forces in a number of directions.

The technique described above for producing a structural strand layerallows for arrangements or configuration of the structural strandswithin the structural strand layer which may be very difficult orimpossible to attain with commercially available stock reinforcingfabrics. In the following figures of FIGS. 19 to 42 further embodimentsof the invention are illustrated in side elevation views only. FIGS. 19to 42 primarily illustrate the layup of the structural strands; theother common components of a fin have been omitted for clarity. Inaddition in FIGS. 19 to 42 the Kevlar strands have been omitted forclarity as well as indicating that they may be considered optional.

In a number of the FIGS. 19 to 42 a core 412 may be shown, but as forthe embodiments disclosed above: the core 412 is an optional component.However in some instances in the below the core may also serve as auseful locational reference where the embodiment may have two structuralstrand layers or arrangements of a structural stand layer continue overtwo layers about the core. An example of a structural strand for theembodiments of FIGS. 19 to 42 may be carbon fibre strands.

FIGS. 19 and 20 are the opposing side elevation views of a fin 1910featuring a structural strand layer with two arrangements. The firstarrangement 1912 has radial structural strands 1912 with a common origin1914 at the intersection of the base 210 and leading edge 214 of the fin1910. Or in other words, the structural strands may extend from onecommon point to form a radial pattern or formation. The secondarrangement 1916 has arc strands 1912 with a common arc centre beingalso the origin 1914. In this structural strand layer the first andsecond arrangements may be laid up either in a non-woven or woven(interlaced) manner to form a scrim. However in comparison tocommercially available reinforcing fabrics there are no substantiallyunidirectional structural strands or structural strands that areorthogonal to each other over their full length of use within thestructural strand layer.

FIGS. 21 and 22 are again opposing side elevation views of a fin 2110.The first arrangement 2112 also has radial structural strands 2112 butwith a virtual origin (not shown) below the base 210. The secondarrangement 2114 is also radial structural strands but with a differentvirtual origin (not shown) which is below the base 210 but forward ofthe leading edge 214.

FIGS. 23A and 23B are again opposing side elevation views of a fin 2310.However this structural strand layer features two arrangements ofpartially continuous radial strands. The first arrangement 2312 ofradial strands originates from a virtual origin (not shown) to the rearof the trailing edge 216. The radial strands 2312 radiate to the base210 and leading edge 214. At the leading edge 214 a portion of theradial strands 2312 are re-directed (or “reflected”) from the leadingedge 214 to form a second arrangement of continuing radial strands 2314that continue to the base 210. This structural strand layer embodimentmay have the effect of providing additional structural strands andconsequently stiffness to the base 210 of the fin 2310 in comparison tothe portion of the fin 2310 towards the tip 218.

FIGS. 24 to 26 illustrate two related fin embodiments 2410, 2510 whereboth structural strand layers originate from the leading edge 214. Thefirst arrangement of structural strands 2412, 2512 radiates to the tipportion 218 of the fins 2410, 2510. The second arrangement 2414, 2514radiates to the base 210 and lower portion of the trailing edge 216.However the second embodiment 2510 employs the use of a core 412 toseparate a first arrangement 2512 from a second arrangement 2514.

FIGS. 27 and 28 are a related embodiment to FIG. 5, however thestructural strand layer for fin 2710 has only one arrangement 2712 ofstructural strands and the strand arrangement is slightly radiused witha substantial portion of the structural strands being in the generaldirection of the sweep 220 of the fin 2710. The fin 2710 also features aportion of uni-directional carbon fibre fabric 418 as described forFIGS. 4 and 5.

FIGS. 29 and 30 are to a fin 2910 embodiment where the structural strandlayer may have two arrangements of structural strands with theindividual strands being continuous through both arrangements. The firstarrangement 2912 of largely parallel structural strands projects in agenerally vertical direction from the base 210 and then executes a foldover 2916 or strand re-direction as produced on the template 610 or thelike. The re-direction 2916 of the structural strands may be such thatthe structural strands again continue in a parallel fashion for thesecond arrangement 2914 directly to the mid section of the trailing edge216. However the second arrangement 2914 features substantially closeradjacent structural strands than for the first arrangement 2912. Such areinforcing layup may not be achievable with commercial reinforcingfabrics.

The stiffness characteristic of the fin 2910 in the region of the secondarrangement 2914 may be higher than that of the region of the firstarrangement 2912 due to the combined effect of the reduced spacingbetween adjacent structural strands together with the overlap betweenthe second 2914 and first 2912 arrangements. Accordingly the fin 2910may have stiffness characteristic of being very stiff towards the baseand in particular for a portion to the mid section of the trailing edge216 but with a particularly flexible or whip-like tip 218. FIG. 30 showsthe presence of a mirror structural stand layer 2912″, 2914″ to FIG. 29,which may further promote the stiffness characteristic described.

FIGS. 31 and 32 illustrate a fin 3110 embodiment with a structuralstrand layer with a first arrangement 3112 and a second arrangement 3114to also vary the stiffness characteristic in different portions orregions of the fin 3110. The first arrangement 3112 of parallelstructural strands may feature a first narrow spacing 3116 and secondlarger spacing 3118 between adjacent structural strands. The firstarrangement 3112 projects from a tip portion 218 towards the base 210along the general sweep angle 220 direction. At a re-direction band 3120the structural strands may be redirected approximately orthogonally asshown. The redirection 3120 may be such that in the second arrangement3114 spacing between adjacent structural strands is uniform. Thisstructural strand layer for fin 3110 may achieve a greater stiffnesscharacteristic for the base portion of the fine 3110 compared with therest of the fin body. This fin 3110 embodiment may have an advantage tothat described with respect to FIGS. 4 and 5 in that the urn-directionalreinforcing fabric 418 may not be necessary.

FIGS. 33 and 34 are to a fin 3310 embodiment similar to that of FIGS. 29and 30; where the structural strand layer may have two arrangements ofstructural strands with the individual strands being continuous throughboth arrangements. However the first arrangement 3312 from the leadingedge 214 portion of the base extends generally towards the tip 218. At are-direction or fold-over band 3316 the first arrangement 3312 istwisted through 180 degrees to form the second arrangement 3314 whichcontinues to the tip 218 as shown.

FIGS. 35 and 34 are to a fin embodiment 3510 with four arrangements ofstructural strands. The first 3512 and second 3514 arrangements may be azigzagged arrangement from one edge of the fin to another edge toapproximately the mid portion of the fin 3510 as shown in FIG. 35. Thefirst 3512 and second 3514 arrangements may be overlayed or interlaced.In FIG. 36 the third 3612 and fourth 3614 arrangements are also shown ina zigzagged fashion, but extending from the mid-portion of the fin 3510to the tip 218.

FIG. 37 is a fin embodiment 3710 where the first arrangement 3712zigzags up the leading edge 214 with one side of the first arrangementinterlaced/woven into the second arrangement 3714 which zigzags up thetrailing edge 216, from base 210 to tip 218.

FIG. 38 is to a fin embodiment 3810 that is an alternate embodiment tothat of FIG. 37. In FIG. 38 the structural strand layer 3812 featureslighter gauge structural strands 3814, 3816 but in a higherdensity/pitch in the weaving/interlacing. This fin 3810 embodiment ofthe structural strand layer may have an increased stiffness to theleading edge 214 but allows the rest of the fin 3810 to twist and flex.

FIGS. 39 and 40 are to a fin embodiment 4010 where a three dimensionalstructural strand layer 3912 may be formed by the use of a templateblock 3910 with a relief machined 3914 into it. The structural strandlayer 3912 may have the individual structural strands 3916 laid up intothe relief 3914. Once all the strands 3916 have been placed a layer ofresin may then be applied to form the three dimensional structuralstrand layer 3912 as a shell. The three dimensional structural standlayer 3912 may then be incorporated into a fin body as describedpreviously; however because of the relief of this structural strandlayer 3912, it may be positioned close to the surface of the fin face310. One or more layers of fibreglass fabric may be located between thefin face 310 surface and the three dimensional structural strand layer3912.

FIGS. 41 and 42 are to another fin embodiment 4110 incorporating anumber of elements from the prior embodiments described above. In thisembodiment 4110 the primary arrangement 4112 of structural strandsgenerally originates from the base 210 of the fin and may then bedirected to the fin leading edge 214. The primary arrangement may thenbe folded over or re-directed at the fin leading edge 214 to thencontinue as the secondary arrangement 4114 of structural strandsproceeding generally to the fin trailing edge 216 as shown. It will bereadily appreciated that the folding over or redirecting from the firstto the secondary arrangement may be achieved using the lay-up template610 described above with respect to FIGS. 6 and 7. For example the foldover or redirection may be slightly offsetted to the fin leading edge asallowed for by use of the lay-up template 610. Alternatively the lay-upmay be with two different carbon strands for each arrangement, theintersection of the strands for the primary and secondary arrangementbeing along all or part of the leading edge of the fin.

The spacings between the structural strands of the primary and secondaryarrangements 4112, 4114 vary from the base 210 to the tip 218 so as toprovide an increased stiffness characteristic towards the base 210 ofthe fin. A reduced spacing of the structural strands towards the baseconsequently increases the stiffness characteristic as well as providinga gradient of the stiffness characteristic across the depth of the fin.

The carbon fibre strands of the secondary arrangement 4114 may belargely perpendicular to the sweep angle of the fin as shown in FIGS. 41and 42. Whilst the carbon fibre strands of the primary arrangement 4112may be offset to the secondary arrangement 4114 by an angle in the rangeof 20 to 40 degrees or preferably approximately 30 degrees.

The primary and secondary arrangements 4112, 4114 of structural strandsmay be analogous to the embodiments of FIGS. 23A, 31 and 35, forexample. The closer spacing of the structural strands towards the finbase 210 may be analogous to FIGS. 23A and 31 for example.

In FIGS. 41 and 42 a core 412 is shown which for this embodiment may beof Lantor Coremat as previously described or any other suitablematerial. In FIGS. 41 and 42 the core 412 is shown on one side of thetwo arrangements 4112, 4114, however as described in detail below thestructural strand arrangements or scrims may be on both sides of thecore 412 as may be used for the centre fin of a thruster configuration,FIG. 1, whilst the single sided structural strand arrangement of FIGS.41 and 42 may be for a side fin of a thruster configuration. In analternate embodiment for a centre fin a scrim/structural strandarrangement may be sandwiched between two cores such that the centre finhas the appearance of FIG. 42 from both sides.

Optionally, another arrangement of largely horizontal, parallelfibreglass strands 4116 may be further included in the fin construction.Alternatively the tertiary arrangement 4116 may use structural strandsof Kevlar or aramide equivalents instead of fibreglass in order toimprove the toughness performance of the fin as well as its stiffnesscharacteristic. The fin embodiment 4110 may be constructed using RTMinjection with vinyl ester as described above.

The embodiments of FIGS. 19 to 42 are also examples of how the spacingand gauge of the structural strands may differ between differentstructural strand layers and between different strand arrangementswithin a structural strand layer.

It will be readily appreciated that elements from the describedembodiments may be used to formulate other embodiments of the inventionand still be within the scope of the invention.

In addition, between side fin/s 124 and centre fin/s 126 of surfboardsthe number and type of structural strand layers may differ. A greaterstiffness characteristic for the centre fin 124 compared with the sidefins 126 may be obtained by the use of a structural strand layerimparting a greater stiffness characteristic and/or multiple structuralstrand layers. For example: to the multiple structural strand layers fora centre fin, two structural strand layers may be used, one on each sideof the core 412. In addition the choice of a core material and thedimensions of the core may also be varied in order to further change thestiffness characteristic or toughness of a fin. It will be readilyappreciated that greater stiffness for a fin may be also achieved bychanging the fin geometry/shape but this would also impact upon thehydrodynamic drag and other hydrodynamic properties.

The above described method and product of using a discrete structuralstrand layer allows the stiffness characteristics in terms of the amountof stiffness and distribution of the stiffness to be readily variedacross the face of the fin and thru the fin body. For example to producea component of twist about the horizontal/longitudinal axis of a fin. Inaddition the deflection and twist characteristics of stiffness may bevaried from one face to the other face of a fin by either the layup ofstrands within an arrangement of a discrete structural strand layerand/or the position of the structural strand layer within constructionof the fin. Fins with customised, multi-axis deflection and twistcharacteristics may be readily produced and tested. The techniquedisclosed here may be suitable for both small experimental andcustom-built production runs common in surf craft fin research anddevelopment work and custom-built professional competition supply aswell as readily adaptable to mass production of a fin product range withparticular stiffness or flexibility characteristics.

For surfboards a fin product range incorporating a structural strandlayer may be, for example, to:

-   -   A surf board rider's proficiency, strength and style of surfing.        For example experienced surfers may prefer a stiffer fin range        to improve surfboard performance. Professional surfers may        require a custom-built fin with a stiffness characteristic        tailored to their particular requirements.    -   A surfboard rider's weight: heavier surfers may require stiffer        fins to maintain hold through turns. The term “hold” is often        used to describe the level of slippage movement of the tail of        the surfboard during turns, particularly aggressive turns.

An example fin product range for surfboards may have the approximatedimensions and angles of:

-   -   “Large”, a depth/height 224 dimension of 119 mm, a base length        226 dimension of 118 mm and a sweep angle 220 of 34 degrees.    -   “Medium”, a depth/height 224 dimension of 113 mm, a base length        226 dimension of 111 mm and a sweep angle 220 of 34 degrees.    -   “Small”, a depth/height 224 dimension of 110 mm, a base length        226 dimension of 105 mm or 109 mm and a sweep angle 220 of 34        degrees.    -   “Custom-Built/Competition”, a depth/height 224 dimension of 119        mm, a base length 226 dimension of 114 mm and a sweep angle 220        of 36 degrees.    -   Sweep angles for surfboard fins according to the invention may        be in the range of 20 to 60 degrees or more preferably in the        range 26 to 56 degrees or in another preferred embodiment        approximately 33 degrees.

A broad, simple example of a stiffness characteristic specification fora fin product range may be the amount of horizontal displacement of thefin tip 218 to an applied force as described above with respect to FIGS.9 to 18. By way of example fins with various structural strand layersmay provide a range in horizontal displacements from 5 to 25 mm or 10 to20 mm of the tip 218 for applied forces typical in variety of surfboarduses.

Without wishing to be bound by theory we believe that the ability toreadily vary the stiffness characteristic across a fin may enablefurther improvements in the performance of a surfboard in the areas of:

-   -   Stall characteristics    -   The hold of the fin/s during a turn and complex manoeuvres.    -   The sensation of “drive”/acceleration into and out of a turn.        Stiffer fins tend produce a greater sensation of drive.    -   The responsiveness of a surfboard may be affected by the        stiffness of the fin/s. Stiffer fins may result in a more        responsive surfboard. A more forgiving surfboard may result from        more flexible fin/s.    -   When transitioning from one turn to another a stiff fin with a        high degree of elastic recoil may provide increased speed and        acceleration from one turn to another as the surfboard        transitions from one side fin to the opposing side fin.    -   Flex: To make a fin that performs more efficiently the inventors        had to ensure it could flex in multiple directions. This        invention's technology is the latest development in fin flexion        which draws on the material lay-up of the fin, the cambered        foil, and the overall fin template. The result is a        multi-directional flex pattern. This unique flex pattern allows        the fin to ‘load-up’ and flex under pressure, and then de-coil        once the pressure is released. Ultimately the fin stores energy        during the transition between turns and then gives it back to        the surfer in the form of superior speed and acceleration. The        feeling can be compared to a slingshot, or whipping effect as        the surfer enters and then exits through the turning arc.    -   Foil: A highly efficient foil in combination with the invention        can be the defining element that makes for exceptional fin        performance. The highly cambered foil in the base of the fin        provides drive and hold, the low cambered foil in the tip        provides stability and allows the fin to release with control,        even when the fin is pushed to the limits. This cambered foil        also increases the fin's stall angle which helps to produce        down-the-line speed and maintain projection through the entire        turning arc.    -   Template: The fin with the invention may feature an efficient,        low aspect ratio elliptical template. The long base increases        drive, moderate volume in the tip enhances the flex and coil        characteristics, and the smooth transitional trailing edge        reduces water separation, which is traditionally linked to        cavitation. Translated, this means increased speed and drive        through minimal water disturbance.    -   Construction: Visually it's easy to see how technology and        performance overlap. Structurally, the fin may draw on a        combination of engineered Bi-axial Carbon (via two arrangements        of uni-directional Carbon) and Uni-directional Kevlar to achieve        the invention's flex pattern. The Uni-directional carbon fibre        fabric (418) base further increases stiffness in the base of the        fin, and helps to distribute pressure away from the plugs (of        the surfboard) by reducing the twisting forces on the fin tabs        securing the fin to the board. The Resin Transfer Moulding (RTM)        process delivers consistency across manufacturing and guarantees        the integrity of the flex and foils. Epoxy resin may be used to        provide strength and material stability, while a lightweight        moulded core further reduces the overall weight of the fin.

It will be readily appreciated that the above described method forreadily altering the stiffness or flexibility properties of a fin of asurfboard may be readily applied to other surf craft such aswindsurfers, paddleboards, wave and surf skis, kite-boarding, wakeboards, and the like.

Although the invention has been herein shown and described in what isconceived to be the most practical and preferred embodiments, it isrecognized that departures can be made within the scope of theinvention, which are not to be limited to the details described hereinbut are to be accorded the full scope of the appended claims so as toembrace any and all equivalent assemblies, devices and apparatus.

In this specification, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise, comprised and comprises” where they appear.

It will further be understood that any reference herein to known priorart does not, unless the contrary indication appears, constitute anadmission that such prior art is commonly known by those skilled in theart to which the invention relates.

1. A fin for surf craft comprising: a fin body; and at least one layerof structural strands, located within the fin body; wherein thestructural strands are in one or more non-woven arrangements; and thestructural strands have a physical property greater than a correspondingphysical property of other material forming the fin body; and whereinthe physical property is selected from at least one of a toughness, atensile strength, an elastic moduli and a Youngs modulus.
 2. A finaccording to claim 1, wherein the fin comprises a base portion and a tipportion and at least a portion of the structural strands extendssubstantially from the base portion to the tip portion of the fin.
 3. Afin according to claim 1, wherein the fin comprises a base portion and aleading edge portion and at least a portion of the structural strandsextends substantially from the base portion to the leading edge portionof the fin.
 4. A fin according to claim 1, wherein the fin comprises aleading edge portion and a trailing edge portion and at least a portionof the structural strands extends substantially from the leading edgeportion to the trailing edge portion of the fin.
 5. A fin according toclaim 1, wherein the fin comprises opposing faces and at least one layerof structural strands in one or more arrangements is located within thefin body such that the at least one layer of structural strands issubstantially parallel to the opposing faces of the fin.
 6. A finaccording to claim 1, wherein the structural strands of at least onelayer are substantially parallel to each other.
 7. A fin according toclaim 6, wherein the fin comprises a sweep angle and, in a firstarrangement, the substantially parallel structural strands are generallyparallel to the sweep angle of the fin.
 8. A fin according to claim 6,wherein the fin comprises a sweep angle and, in a first arrangement, thesubstantially parallel structural strands are at a first angle to thesweep angle of the fin, the first angle being in the range of up to 20degrees.
 9. A fin according to claim 8, the first angle is approximately10 degrees.
 10. A fin according to claim 6, wherein, in a secondarrangement the substantially parallel structural strands are at asecond angle to the vertical of the fin, the second angle being in therange of 20 to 40 degrees.
 11. A fin according to claim 6, wherein thefin comprises a vertical component and, in a second arrangement, thesubstantially parallel structural strands are at an angle ofapproximately 30 degrees to the vertical of the fin.
 12. A fin accordingto claim 6, wherein, in a third arrangement, the substantially parallelstructural strands are generally vertical.
 13. A fin according to claim6, wherein the fin comprises a sweep angle and, in a primaryarrangement, the substantially parallel structural strands are generallyperpendicular to a sweep angle of the fin.
 14. A fin according to claim13, wherein, in a secondary arrangement, the substantially parallelstructural strands are at a first angle to a sweep angle of the fin, thefirst angle being in the range of 20 to 40 degrees.
 15. A fin accordingto claim 13, wherein, in a secondary arrangement, the substantiallyparallel structural strands are at a first angle of approximately 30degrees to a sweep angle of the fin.
 16. A fin according to claim 13,wherein, in a tertiary arrangement, the substantially parallelstructural strands are generally vertical.
 17. A fin according to claim1, wherein at least one layer of structural strands comprises of aplurality of structural strands extending from at least onesubstantially common point in a substantially radial formation.
 18. Afin according to claim 17, wherein the fin comprises a base portion andthe at least one substantially common point is adjacent the base portionof the fin.
 19. A fin according to claim 17, wherein the fin comprises aleading edge portion and a trailing edge portion and the at leastsubstantially common point is adjacent at least one of a leading edgeportion and a trailing edge portion of the fin.
 20. A fin according toclaim 1, wherein at least one structural strand comprises of a pluralityof filaments.
 21. A fin according to claim 1, wherein at least onestructural strand is made of at least one of carbon fibre, Kevlar,aramide, natural fibres and synthetic fibres.
 22. A fin according toclaim 1, wherein at least one structural strand has a tensile strengththat is at least 1.5 times greater than the tensile strength of theother material forming the fin body.
 23. A fin according to claim 1,wherein at least one structural strand has a Youngs modulus that is atleast 1.5 times greater than a Youngs modulus of the other materialforming the fin body.
 24. A fin according to claim 1, wherein at leastone structural strand has a toughness that is greater than a toughnessof the other material forming the fin body.
 25. A fin according to claim1, wherein at least a portion of the structural strands comprisesunidirectional filaments in a ribbon configuration.
 26. A fin accordingto claim 1, wherein at least a portion of the structural strands have awidth in the range of 0.5 to 3 mm.
 27. A fin according to claim 1,wherein at least a portion of the structural strands has a width in therange of 1 2 mm.
 28. A fin according to claim 1, wherein at least aportion of the structural strands comprises of at least about 3,000filaments per structural strand.
 29. A fin according to claim 1, whereinthe fin comprises a base portion and a tip portion and a spacing betweenat least a portion of the structural strands is less towards the baseportion compared with the tip portion of the fin.
 30. A fin according toclaim 1, wherein a spacing between at least a portion of the structuralstrands is in the range of 1 to 30 times a width of one structuralstrand.
 31. A fin according to claim 30, wherein a spacing between atlest a portion of the structural strands is in the range of 4 to 13times a width of one structural strand.
 32. A fin according to claim 1,wherein a spacing between at least a portion of the structural strandsis in the range of 4 to 15 mm.
 33. A fin according to claim 32, whereina spacing between at least a portion of the structural strands is in therange of 9 to 13 mm.
 34. A fin for surf craft comprising: a fin body;and at least one layer of structural strands, located within the finbody; wherein the structural strands are in one or more wovenarrangements that are at least one of an open weave and a scrim; whereinthe structural strands have a physical property greater than acorresponding physical property of other material forming the fin body;and wherein the physical property is selected from at least one of atoughness, a tensile strength, an elastic moduli and a Youngs modulus.35. A fin according to claim 34, further including a core structurelocated within the fin body.
 36. A fin according to claim 35, wherein atleast one layer of structural strands in one or more arrangements isembedded within a body of the fin such that the layer of structuralstrands is substantially parallel to a face of the core structure.
 37. Afin according to claim 35, wherein the fin comprises opposing faces andthe at least one layer of structural strands are located intermediatethe core structure and at least one of the opposing faces of the fin.38. A fin according to claim 35, wherein the core is at least one of afoam core structure and a solid, non-foam core structure.
 39. A finaccording to claim 35, wherein at least a portion of the core structureis made of at least one of PVC foam, polyurethane foam, resinimpregnated fibreglass, hardened resin, polyester mat, microspheres,plastic, bamboo and wood.
 40. A fin according to claim 34, wherein thefin body comprises a base portion and further includes at least onelayer of unidirectional carbon fibre fabric towards the base portion ofthe fin body.
 41. A fin according to claim 40, wherein the at least onelayer of carbon fibre fabric is located about a periphery of the finbody.
 42. A fin according to claim 34, having a sweep angle of from 20to 60 degrees.
 43. A method of controlling a fin physical property for asurf craft, the method comprising: selecting one or more structuralstrands having a structural strand physical property greater than acorresponding physical property of other materials in a body of the fin;selecting a number of structural strands to provide the fin physicalproperty; providing a layer of the structural strands in one or morearrangements; and embedding the layer of structural strands in the bodyof the fin; whereby varying at least one of the structural strandsselection, the number of structural strands or the arrangement of thestructural strands varies the fin physical property; and wherein the finphysical property is selected from at least one of: a stiffnesscharacteristic, a bending resistance, a twisting resistance, aresistance to a deflection, a flexibility and a high elastic recoil; andwherein the structural strand physical property is selected from atleast one of: a toughness, a tensile strength, an elastic moduli and aYoungs modulus.
 44. A method according to claim 43, wherein the step ofproviding a layer of structural strands includes the use of a templateto locate one or more structural strands of one or more arrangements.45. A method according to claim 44, wherein the step of using a locatingtemplate further includes providing at least one of pins, adherents andsecuring systems to locate one or more structural strands.
 46. A methodaccording to claim 44, wherein the step of using a locating templatefurther includes the steps of: providing one or more reliefs machinedinto the template, and laying individual structural strands intorespective reliefs to form a three dimensional structural strand layer.47. A method according to claim 44, wherein the step of providing alayer of structural strands includes the use of a numerically or acomputer controlled machine to locate one or more structural strands ofone or more arrangements.
 48. A method according to claim 43, whereinthe step of providing a layer of structural strands further includes astep of: configuring the arrangement of structural strands in a layer tovary the fin physical property.
 49. A method according to claim 43,further including providing one or more structural strands largelyparallel to a sweep angle of the fin such that the fin is provided withan increased resistance to a twisting of the fin.
 50. A method accordingto claim 43, further including providing one or more structural strandsat a first angle of up to 20 degrees to a sweep angle of the fin toprovide the fin with an increased resistance to a twisting of the fin.51. A method according to claim 43, further including providing one ormore structural strands at a second angle in the range of 20 to 40degrees to the vertical axis of the fin such that the fin is providedwith an increased resistance to a deflection from the vertical axis 52.A fin for surf craft produced according to the method of claim
 43. 53.(canceled)
 54. (canceled)